The operation of expansion machines, such as steam turbines or displacement machines, e.g. piston engines, by means of the Organic Rankine Cycle (ORC) method for the generation of electric energy through the use of organic media, e.g. organic media having a low evaporation temperature, which generally have higher evaporation pressures at the same temperatures as compared to water as working medium, is known in the prior art. ORC plants constitute a realization of the Rankine cycle in which electric energy is basically obtained, for example, by means of adiabatic and isobaric changes of condition of a working medium. Mechanical energy is generated by the evaporation, expansion and subsequent condensation of the working medium, and is converted into electric energy. Basically, the working medium is brought to an operating pressure by a feed pump, and energy in the form of heat, which is provided by a combustion or a flow of waste heat, is supplied to the working medium in a heat exchanger. The working medium flows from the evaporator through a pressure pipe to an expansion machine of an ORC system where it is expanded to a lower pressure. Subsequently, the expanded working medium vapor flows through a condenser in which a heat exchange takes place between the vaporous working medium and a cooling medium. Then, the condensed working medium is fed by a feed pump back to the evaporator in a cycle.
The advantage of using Organic Rankine Cycle systems, in particular for the utilization of low-temperature heat, is sufficiently known. Particularly in the range of relatively small system powers, for example in the range of 1 kW to approximately 50 kW, displacement machines are used frequently. These displacement machines may be piston engines. These machines need a certain amount of oil as lubricant in the machine. In the machine cycle the oil in the cycle usually circulates together with the working medium. In doing so, the oil particularly also passes the condenser of the system, which may result in an higher pressure loss in the condensation.
Condensers used in the field of refrigeration engineering and air conditioning technology, so-called liquefiers, can be regarded as prior art. In refrigeration engineering vapor is condensed after the compression at a high pressure and a relatively high temperature. The vapor, when entering the condenser, has a relatively high density. In order to obtain sufficiently high flow speeds the vapor volume flow is distributed to a few pipelines which then run through the individual levels of the condenser.
The condenser typically has an inlet and an outlet between which the pipelines are arranged, in which the major part of the condensation takes place. Often, the pipes of the pipelines are arranged substantially horizontally. In horizontal arrangements the condensate furthermore requires a driving force so as to flow to the outlet of the condenser. To this end, the vapor and the condensate have to flow in a parallel flow. The condensate is “blown” by the vapor through the pipes. The transport of the condensate by means of the vapor requires energy. This results in a pressure loss inside the condenser, and the pressure loss between the entry of the vapor into the condenser and the discharge of the condensate can be measured. The pressure loss increases quadratically with the flow speed of the vapor in a turbulent flow. Moreover, the pressure loss depends on the viscosity of the liquid. In particular, the pressure loss increases with the viscosity of the liquid.
The above-mentioned oil in the displacement machines is used, for example, for lubricating flanks and bearings. In other words, components gliding along one another and/or rolling upon one another are lubricated. The oil takes part in the machine cycle. One can furthermore talk about a fluid representing a mixture of the actual working medium of the machine and the oil, respectively an oil-containing liquid.
The oil passes the expansion machine jointly with the vapor, and is discharged from the expansion machine, for example, in the form of an oil-vapor spray or oil-vapor mist. That is, liquid is already contained in the vapor at the inlet of the condenser, meaning while the greater portion of the vapor is still present in the form of a vaporous working medium, one portion of the vapor is already mixed, at least partially, with oil-containing liquid droplets upon entering the condenser or even upstream of the inlet into the condenser. At the beginning, i.e. near the inlet of the condenser, only little condensate is separated, the oil portion in this condensate being very high. Practically, it is almost pure oil. Correspondingly, the viscosity of this separated liquid is very high. This may entail very high pressure losses, which are disadvantageous for the condenser. These pressure losses may, again, reduce the performance of the entire system, in particular of the expansion machine, so that eventually the efficiency of the process as a whole is reduced. This may result in performance losses in the two-digit percent range.
In comparison with the air conditioning technology the working medium particularly in ORC systems is condensed at lower pressures. That is, the vapor has a lower density. A clearly greater volume flow is achieved with similar mass flows and condensation performances. With an identical construction of the condenser this stands for a greater speed of the vapor and, thus, clearly greater pressure losses.
An improvement of the condensation and a reduction of the pressure losses can be achieved by a more frequent division of the vapor volume flow. The problem of having oil or oil-like or oil-containing liquids in the system and pressure losses associated therewith persists, however.
Given the above-outlined problem in the prior art it is the object of the present invention to provide a device and a method for the condensation of vapor of an expansion machine of a thermal power plant, expanded in an expansion machine of a thermal power plant, so that the above-outlined disadvantages can be reduced or even eliminated and the performance losses associated therewith can be reduced or even overcome.